Boiler combustor side blockage detection system and method

ABSTRACT

Disclosed is a boiler blockage detection system and method utilizing inputs from a pressure sensing elements. A logic circuit may determine a boiler firing rate based on an input signal from the combustion controller. An indication of the exhaust pressure level and an indication of the inlet pressure level are received. A pressure differential between the exhaust pressure level and the inlet pressure level is determined. Alternatively, a pressure differential transmitter may determine the pressure differential. The determined pressure differential is compared to a predetermined pressure level differential threshold. The predetermined pressure level differential threshold is dependent on the determined firing rate. Based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold, it may be determined that there is a blockage of an intake or an exhaust of the boiler. In response to the blockage determination, an interrupt signal is output.

This application claims the benefit of priority to provisional Application Ser. No. 62/634,381 filed Feb. 23, 2018, which is incorporated herein by reference in its entirety.

BACKGROUND

In residential and commercial boilers and water heaters and similar appliances, especially those with high turndown ratios, there are sometimes conditions in which combustion air flow to the appliance may be restricted due to blockage of the air inlet duct that delivers air to the appliance, blockage of the exhaust duct that delivers exhaust from the appliance, fouling of the heat exchanger of the appliance, or component failure, among other possible conditions. Unlike industrial and utility boiler systems, which are generally custom engineered and continuously monitored, residential and commercial boilers may be packaged units preferably capable of operating under a range of operating conditions and system configurations without operator attention.

Therefore, there is a need for improved systems and methods for detection of blockages in inlet air and/or exhaust gas flow in appliances such as commercial and residential boiler/water heater systems.

SUMMARY

To improve the blockage monitoring accuracy and operational control of residential and commercial high-turn ratio boiler systems as well as provide other benefits, disclosed is a blockage detection method and blockage detection system that may be used with a commercial/residential boiler or water heater that provides improved blockage detection and shutdown of a combustion process.

An example of a system for detecting blockage of air entering a boiler or exhaust gas exiting the boiler includes an exhaust pressure sensing element, an inlet pressure sensing element, a relay, and a logic circuit. The logic circuit may be coupled to the exhaust pressure sensing element, the inlet pressure sensing element, and the relay, and may be configured to be coupled to a combustion controller of the boiler. The exhaust pressure sensing element may be configured to be coupled to the boiler and to detect an exhaust pressure level in the exhaust of a boiler. The inlet pressure sensing element may be configured to be coupled to the boiler and to detect an inlet pressure level in air entering the boiler. The logic circuit may be configured to determine a firing rate of the boiler based on an input signal received from the combustion controller. The logic circuit may further determine a pressure differential between the exhaust pressure level detected by the exhaust pressure sensing element and the inlet pressure level detected the inlet pressure sensing element. The determined pressure differential may be compared by the logic circuit to a predetermined pressure level differential threshold. The predetermined pressure level differential threshold being dependent on the firing rate. Based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold, the logic circuit determines whether a boiler duct is at least partially blocked. Based on a determination that the boiler duct is at least partially blocked, an interrupt signal is output. The relay may be coupled to the logic circuit. The relay may be configured to receive the interrupt signal from the logic circuit, and upon receipt of the interrupt signal, interrupt power to the combustion controller to shut down a combustion process of the boiler system.

Provided is another example of a system for detecting blockage of air entering a boiler or exhaust gas exiting the boiler. This system example includes a differential transmitter, a logic circuit and a relay. The differential pressure transmitter may be configured to detect a differential pressure across a boiler, and output a pressure differential signal indicating the detected differential pressure across the boiler. The logic circuit may be coupled to the differential pressure transmitter. The logic circuit being configured to receive the pressure differential signal from the differential pressure transmitter. The pressure differential signal is compared to a predetermined pressure level differential threshold. Based upon a result of the comparison of the pressure differential signal to the predetermined pressure level differential threshold, the logic circuit is configured to determine whether there is at least a partial blockage of a boiler duct. In response to a determination of the at least partial blockage, an interrupt signal is output. The relay is coupled to the logic circuit. The relay is configured to halt a combustion process of the boiler in response to receiving the interrupt signal.

Provided is an example of a method of detecting a blockage in a boiler system. The example method may include determining by a logic circuit a firing rate of the boiler system based on an input signal received from a combustion controller of the boiler system. An indication of the exhaust pressure level and an indication of the inlet pressure level are received. A pressure differential between the exhaust pressure level and the inlet pressure level is determined. The determined pressure differential is compared to a predetermined pressure level differential threshold. The predetermined pressure level differential threshold is dependent on the determined firing rate. Based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold, it may be determined that there is at least a partial blockage of an intake duct or an exhaust duct of the boiler. In response to the blockage determination, an interrupt signal is output.

Provided is an example of a boiler system configured for detecting blockage of air entering the boiler system or exhaust gas exiting the boiler system. The example boiler system may include a boiler, an exhaust pressure sensing element, an inlet pressure sensing element, a logic circuit, and a relay. The boiler may include a combustion controller and a boiler duct. The exhaust pressure sensing element may be coupled to the boiler and may be configured to detect an exhaust pressure level of exhaust gas exiting the boiler. The inlet pressure sensing element may be coupled to the boiler and may be configured to detect an inlet pressure level of air entering the boiler. The logic circuit may be coupled to the exhaust pressure sensing element and the inlet pressure sensing element and the combustion controller. The logic circuit may be configured to determine a firing rate of the boiler based on an input signal from the combustion controller. The logic circuit may be configured to determine a pressure differential between the exhaust pressure level detected by the exhaust pressure sensing element and the inlet pressure level detected the inlet pressure sensing element, and compare the determined pressure differential to a predetermined pressure level differential threshold. The predetermined pressure level differential threshold may be dependent on the firing rate. The logic circuit may determine whether the boiler duct is at least partially blocked based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold. The logic circuit, based on a determination that the boiler duct is at least partially blocked, outputs an interrupt signal. The relay may be coupled to the logic circuit. The relay may be configured to receive the interrupt signal from the logic circuit, and in response to receiving the interrupt signal, interrupt power to the combustion controller to shut down a combustion process of the boiler system.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations in accord with the present concepts, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.

FIG. 1 depicts an example of a boiler system configured with an example of an intake/exhaust blockage detection system as described herein.

FIG. 2A shows an example of a controller suitable for use as the pressure interlock controller of FIG. 1.

FIG. 2B shows another example of a controller suitable for use as the pressure interlock controller of FIG. 1.

FIG. 3 illustrates examples of system pressure operating curves for use in explaining the benefits of the described examples.

FIG. 4 illustrates an example of how duct blockage effects system performance.

FIG. 5 illustrates an example of a process flow for detecting an intake or exhaust blockage.

It should be understood that, while the accompanying figures illustrate examples that include the portions of the disclosure claimed, and explain various principles and advantages of those examples, the details displayed are not necessary to understand the illustrated examples, as the details depicted in the figures would be readily apparent to those of ordinary skill in the art having the benefit of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

During operation of a boiler/water heater, a control system, a separate controller or a device monitors the water temperature and adjusts the thermal input to maintain the water temperature at a desired temperature setting. The thermal input is varied by changing the combustion blower speed, fuel pressure and/or air and fuel flow control valves. The control signal or signals that sets this thermal input is generally, and for this discussion, called the firing rate. In a modulating boiler, the firing rate is continuously changing during the operation of the boiler/water heater.

A blockage may be detected by pressure switches which monitor overall system pressure drop or pressure drop across a fixed orifice. At 20 to 1 turndown the corresponding pressure drop change can be as high as 400 to 1 possibly exceeding the sensitivity of available pressure switches that can result in an inability of the control system to accurately monitor and safely control operation of the boiler system.

Through the measurement of the system pressure drop and the comparison of this value to a pre-defined allowable pressure, improved blockage protection can be achieved at turndown ratios of 20 to 1 and greater. The acceptable maximum pressure drop value is tied to the firing rate of the boiler to ensure a continuous protection over the boiler operating range. The acceptable maximum pressure drop versus firing rate can be obtained from a pre-defined look-up table or algorithm for the boiler type and size and fuel type. When the measured pressure drop exceeds the pre-defined allowable pressure, a safety interlock can be activated to shutdown the boiler, thereby enhancing the safety of the system.

Reference now is made in detail to the examples illustrated in the accompanying drawings and discussed below.

FIG. 1 shows an example of a water heater/boiler system implementing an example of an intake/exhaust blockage detection system. The boiler system 100 may include a boiler 30 having a combustion chamber 32 and a boiler duct (combined air inlet pathway 40 and exhaust variable length duct 16).

The water heater/boiler 30 may include a series of tubes 1 that may, for example, have water circulating within the tubes 1 and hot gases within combustion chamber 32 from a combustor 2 passing over the outside of the tubes 1. The tubes 1 may or may not have extended heat exchange surfaces (not shown) on the inside and/or outside of the tubes 1. The tubes 1 may be attached to an inlet header 21 and an outlet 22 header that respectively distribute and collect the water (not shown) that is circulated via a water pump 14. Alternatively, the combustion chamber 32 may be omitted and a water tank may be utilized that holds water, in which case, the water may be on the outside of the tubes and the combustion gases on the inside of the tubes 1.

The combustor 2 receives a mixture of fuel and air from a fuel delivery system (described in more detail below) and disperses the ignited mixture (i.e. combustion products that generate heat) into the combustion chamber 32 which enable the exchange of heat with the tubes 1. The thermal energy from the combustion products is transferred to the water through the tube 1 walls and the combustion products after transferring heat to the tubes 1 are exhausted from the combustion chamber 32 at a much reduced temperature. The foregoing description is for ease of discussion, but of course other configurations, such as single or multi-pass water and combustion product geometries are possible. When the combustion products are being exhausted from the combustion chamber 32, the combustion products may be collected in some form of exhaust outlet 33. The exhaust outlet 33 may be connected to an exhaust variable length duct 16 that conveys the cooled combustion products to the environment. The cooled combustion products may or may not give up some of the latent heat remaining with the cooled combustion products, and therefore some of the moisture generated in the combustion process may leave the boiler in the form of water through a condensate outlet and trap 23.

The fuel and air delivery system in this example may include a blower 3, an air inlet pathway 40, a motor 4, a pilot flame 1, and a fuel gas pressure regulator 8 and automatic shutoff valve 9. The fuel gas may be supplied from a holding tank or some other fuel gas supply. Of course, other fuel sources besides gas may also be used. The blower 3 may create a suction pressure that draws air in through an air inlet pathway 40. The air inlet pathway 40 may include the air duct 15 and the filter 7. The air duct 15 of the air inlet pathway 40 may, for example, be connected to an outdoor air supply or may terminate within the building housing the system. The air may be drawn through a filter 7 to remove particulates. The suction pressure created by the blower 3 may be adjusted, for example, by using a venturi 6 or other mixing device that draws in a metered quantity of fuel gas via a fuel gas pressure regulator 8 and automatic shutoff valve 9. The thermal input to the water heater 30 is a function of the blower 3 speed which is adjusted by regulating the power to the motor 4 via a variable speed drive 5.

The fuel and air mixture can be ignited directly with a spark or a hot surface ignition source or via a pilot flame 20. The pilot flame 20 may be ignited prior to the main gas valve 9 opening. The pilot flame 20 typically has its own automatic shutoff valve 10 and fuel pressure regulator 11. There are many different methodologies for detecting the ignition of the pilot flame 20 and/or main combustor flame and their use is not limited by the presently described examples. Likewise, there are many embodiments of the fuel and air delivery system to accomplish the metering and mixing of the main air and fuel flows. In alternate examples, in addition to the blower speed being adjusted, air and fuel dampers and/or pressure regulators may be adjusted to regulate the air and fuel flow rates. In these various examples, a combustion controller 12 may determine the settings of the various devices (e.g., variable speed drive 5, main gas valve 9 and the like) based the temperature of the water leaving the water heater 30 (e.g. detected by a temperature sensing device, such as a thermocouple, thermostat, or the like) as well as other factors which determine the required thermal input from the combustor 2.

For example, the combustion controller 12 may include a processor, a memory, and input/output terminals (not shown) as are known in the art of boiler control systems. The combustion controller memory may store program code executable by the processor. The combustion controller 12 processor may process inputs to the controller 12 received via the input terminals, such as water temperature, the boiler safety chain 13, such as safety circuit interrupt 59, and/or the like. The combustion controller 12 processor may output signals such as firing rate and process parameters via the output terminals.

The combustor controller 12 may further include, be enabled or powered by, a boiler safety chain 13. The boiler safety chain 13 may be an electrical circuit formed from a number of different relays (shown, for example, as relays 71, 72, 73) configured to halt or prohibit operation of the combustor 2 if unsafe conditions exist or occur during operation of the boiler system 100. Examples of devices that may make up the safety chain 13 may include a low water level cut out device, a high water temperature cutout device, low and high fuel pressure responsive switches, water flow responsive switches, and the like. In some examples, the relays 71-73 may be implemented as a logic as part of the logic circuit executed by the combustion controller 12, in particular, if the combustion controller 12 is performing the pressure calculations and comparison to a predetermined differential pressure threshold.

An example of the advantageous intake/exhaust blockage detection system as described herein may include a pressure interlock controller 19 and associated pressure sensing elements 17 and 18. Examples of a pressure sensing elements 17 and 18 may include a piezoelectric device, a mechanical diaphragm coupled to a strain gauge, differential capacitance, or the like, that generates an electrical signal or alters an applied electrical current/voltage in response to changes in pressure.

The pressure interlock controller 19 and associated pressure sensing elements 17 and 18 are used to monitor the pressure differential across the boiler system 100 and to interrupt the safety chain when the system is operating outside of prescribed limits. The pressure differential is the difference between the measured pressures (or difference between the representation of the measured pressures) based on the outputs from the pressure sensing elements 17 and 18. The threshold of the pressure differential may be related to the firing rate of the water heating system. For example, the threshold pressure for a given boiler type, size and fuel may be determined empirically but may also be determined through calculation including computational fluid dynamics analysis. The pressure sensing elements 17 and 18 may be located along the respective boiler ducting so that a differential pressure from the air inlet duct 15 and the exhaust duct 16 may be measured directly, and/or calculated. The pressure sensing elements 17 and 18 may measure the total pressure or the static pressure depending on the sensing element location. The total pressure may be the sum of the static pressure and the stagnation pressure.

In more detail, the pressure sensing element 18 may be referred to as an exhaust pressure sensing element. The exhaust pressure sensing element 18 may, for example, be configured to be coupled to the boiler 30 near the exhaust pathway that includes the exhaust outlet 33 and the exhaust variable length duct 16. For example, the exhaust pressure sensing element 18 may be affixed at some point along the exhaust outlet 33 and the exhaust variable length duct 16. The exhaust pressure sensing element 18 may be configured to detect an exhaust pressure level in the exhaust outlet 33 and the exhaust variable length duct 16 as the exhaust gas exits the boiler system 100.

The pressure sensing element 17 may be referred to as an inlet pressure sensing element. The inlet pressure sensing element 17 may be configured to detect an inlet pressure level of air (or other gas) entering, for example, via the air inlet pathway 40 of the boiler system 100. For example, the inlet pressure sensing element 17 may be coupled to the boiler 30 near the air inlet pathway 40, for example, after the filter 7.

The exhaust pressure sensing element 18 and the inlet pressure sensing element 17 may be coupled to the pressure (labeled as “Press”) interlock controller 19. The pressure interlock controller 19 may also be coupled to the combustion controller 12. The pressure interlock controller 19 may include a logic circuit (described in more detail with reference to FIG. 2) that provides control and other functions in response to inputs. The pressure interlock controller 19 is configured to accept inputs from the exhaust pressure sensing element 18 and the inlet pressure sensing element 17. The respective pressure sensing elements 17 and 18 may, for example, be configured to provide digital or analog electrical signals indicative of the inlet air pressure and the exhaust gas pressure, respectively, to the pressure interlock controller 19. For example, the pressure interlock controller 19 may have input terminals for receiving the respective electrical signals. Alternatively or in addition, the respective pressure sensing elements 17 and 18 may include tubes (not shown) that allow for the conveyance of exhaust gas pressure and air inlet pressure to pressure sensing elements located at the pressure interlock controller 19. For example, the pressure interlock controller 19 may be configured with ports and associated electro-mechanical components (not shown in this example), such as transducers or the like, that generate, for example, electrical signals in response to the application of positive or negative air/gas pressure via tubing or the like coupled to the ports.

As described in more detail with reference to FIGS. 2A, 2B and 5, the pressure interlock controller 19 upon determination that at least a partial blockage capable of potentially causing increased carbon monoxide is present may generate a safety circuit interrupt 59 either by actuation of a relay (not shown) within the pressure interlock controller 19 or an external relay. In an example in which the relay is within the pressure interlock controller 19, the relay may be part of the boiler safety chain 13. Alternatively, the safety circuit interrupt 59 may be output from the pressure interlock controller 19 and received as an input to a relay, such as 71, 72 or 73, that is part of the boiler safety chain 13. For example, the relay 71 may be configured to receive the inputted interrupt signal and actuate in response to the inputted safety circuit interrupt 59. The interrupt signal may remove power to the relay device as an effective means of providing the interrupt.

The system 100 may also include audio/visual output device 288. The audio/visual output device 288 may be, for example, a buzzer, a speaker, a light emitting diode, a strobe light, a combination audio-visual indicator device, or the like. The audio/visual output device 288 may be coupled to the pressure interlock controller 19, or, alternatively, coupled to the combustion controller 12.

FIG. 2A shows an example of a controller suitable for use as, for example, as the pressure interlock controller of FIG. 1. An example of the controller 200 may include a logic circuit 210, a power supply 220, a memory 230 and a storage 240. Within the controller 200, the logic circuit 210 is coupled to the power supply 220, the memory 230 and the storage 240.

The logic circuit 210 may be a processor, a field programmable gate array (FPGA), or other configuration of electronic circuitry that is configured to perform functions. The logic circuit 210 may include other components for processing of input signals or output signals. For example, the logic circuit 210 may optionally include an analog-to-digital converter (A/D) 215 for converting analog input signals received from the respective pressure sensing elements 17 and 18. In addition, the logic circuit 210 may include an amplifier (not shown) for amplifying the safety circuit interrupt signal prior to output. The logic circuit 210 may also be coupled to audio and/or visual output device 288. For example, the logic circuit 210 may be configured to output an alarm signal for generating an audible and/or visual indication indicating one or more of: a partially blocked inlet air duct 15, a partially blocked exhaust duct 16, a fouling of a heat exchanger component, a fouling of a combustor component (e.g., 2, 20, 3 and 32), improper sizing of a variable length duct (e.g., 15 or 16), or an improper sizing of a duct termination 36. Alternatively, the alarm signal may be delivered to the combustion controller 12, which may then actuate the audio/visual output device 288.

The power supply 220 may be a DC power supply configured to receive AC or DC electricity that is transformed/converted and conditioned to provide DC power suitable for the electronics of the logic circuit 210, the memory 230 and/or the storage 240.

The storage 240 may be configured to maintain data generated by the logic circuit 210. The storage 240 may be an electrically erasable programmable read only memory (EEPROM), a FLASH memory, non-volatile random access memory (RAM), or other form of data storage device. The storage 240 may, for example, be configured to store calculations of the differential pressure performed by the logic circuit 210, or other information.

The memory 230 may be a non-volatile memory, and may be configured to store program code 237 suitable for execution by the logic circuit 210. For example, the memory 230 is shown coupled to the logic circuit 210. The memory 230 may store a predetermined pressure level differential threshold and program code. The logic circuit 210 may be configured to perform functions upon execution of the program code 237 stored in the memory.

The program code 237 when executed by the logic circuit 210 may configure the logic circuit 210 to receive, process and respond to input signals. For example, the input signal from the combustion controller 12 may indicate the firing rate used by the boiler 100 to the logic circuit 210. The input from the exhaust sensing element 18 is representative of the exhaust gas pressure level, and the input from the inlet pressure sensing element 17 is representative of the air inlet (or intake) pressure level.

The safety circuit interrupt, such as 59 of FIG. 1, may be output to an optional relay, such as 249, integrated with the controller 200. While described as integral to the controller 200, the relay 249 may be located external to the controller 200. The relay 249 may be coupled to the logic circuit 210 of the pressure interlock controller 200, and in series or parallel with relays 71-73 of the safety chain 13 of combustion controller 12. The relay 249 may be configured, in response to receiving the interrupt signal from the logic circuit, to halt a combustion process controlled by the combustion controller 12. For example, upon receipt of the interrupt signal from the logic circuit 210, the relay 249 may interrupt power provided by the safety chain 13 circuit of the combustion controller 12 causing the combustion process controlled by the combustion controller 12 to shut down.

The logic circuit 210 may further be configured to output an alarm signal for generating an audible and/or visual indication to an audio/visual output device 288. The alarm signal may indicate one or more of: a partially blocked inlet air duct, a partially blocked exhaust duct, a fouling of a heat exchanger component, a fouling of a combustor component, improper sizing of a duct, or an improper sizing of a duct termination. Alternatively, the alarm signal may be delivered to the combustion controller 12, which may then actuate the audio/visual output device 288

Alternatively, a controller suitable for use as a pressure interlock controller may be configured as shown in FIG. 2B. The controller 201 may include a logic circuit 211, a power supply 220, a memory 231, a storage 241 and an analog to digital (A/D) converter 215. Within the controller 201, the logic circuit 211 is coupled to the power supply 221, the memory 231 and the storage 241. The logic circuit 211 may be a processor, a field programmable gate array (FPGA), or other configuration of electronic circuitry that is configured to perform functions. The logic circuit 211 may include other components for processing of input signals or output signals. For example, the logic circuit 211 may optionally include an analog-to-digital converter (A/D) 215 for converting analog input signals received from the respective pressure sensing elements 17 and 18. In addition, the logic circuit 211 may include an amplifier (not shown) for amplifying the safety circuit interrupt signal prior to output. The power supply 220 may be a DC power supply configured to receive AC or DC electricity that is converted and conditioned to provide power suitable for the electronics of the logic circuit 211, the memory 231 and/or the storage 241.

The memory 231 may be a non-volatile memory, and may be configured to store program code 238 suitable for execution by the logic circuit 211. The storage 241 may be configured to maintain data generated by the logic circuit 211. The storage 241 may be an electrically erasable programmable read only memory (EEPROM), a FLASH memory, non-volatile random access memory (RAM), or other form of data storage device. The storage 241 may, for example, be configured to store calculations of the differential pressure performed by the logic circuit 211, or other information.

In the example of FIG. 2B, the exhaust duct 16 and the intake duct 15 as part of the air inlet pathway 40 may be coupled to a differential pressure transmitter 214, and the differential pressure transmitter 214 may provide a differential pressure signal that is received by the logic circuit 211. For example, the exhaust duct 16 and the intake duct 15 may be configured to accept tubing that allows for direct measurement of pressures within the respective ducts 15 and 16. The differential pressure transmitter 214 may be configured with input ports that couple to the tubing connected to the respective intake duct 15 and the exhaust duct 16. In response to the respective pressure input from the intake duct 15 and the exhaust duct 16, the differential pressure transmitter 214 may be configured to generate an electrical signal indicative of the differential pressure between the relative pressures in the intake duct 15 and the exhaust duct 16 that may be output to the logic circuit 211. For example, the differential pressure may be detected based differences between an intake pressure at an air intake duct, which is also referred to as the inlet duct, and an exhaust pressure of the boiler at the exhaust outlet duct. The differential pressure transmitter 214 may be further configured, upon detecting the differential pressure, to output a pressure differential signal indicating the detected differential pressure across the boiler or water heater.

The logic circuit 211 receives and processes the outputted pressure differential signal. For example, the logic circuit 211 may be configured to execute the program code 238 and process the received pressure differential signal to determine that the received pressure differential signal indicates a negative pressure when an inlet duct is at least partially blocked, and indicates a positive pressure when the exhaust duct is at least partially blocked. The pressure differential signal provided by the differential pressure transmitter 214 may be an analog signal. The logic circuit 211 may be configured to perform the comparison between measured system pressure differential and the pre-determined pressure differential using analog circuitry.

The safety circuit interrupt signal, such as 59 of FIG. 1, may be output to a relay 249, which may be a relay in the safety chain 13 of FIG. 1, for example, such as one of relays 71-73 of FIG. 1. The relay 249 may be coupled to both the logic circuit 211 of the pressure interlock controller 201 and the combustion controller 12. The relay 249 may be configured, in response to receiving the safety interrupt signal 59 from the logic circuit, to cause the combustion controller 12 to halt a combustion process controlled by the combustion controller 12. For example, upon receipt of the interrupt signal from the logic circuit 211, the relay 249 may interrupt power to a safety chain circuit, such as 13, of the combustion controller 12 causing the shut down the combustion process.

The logic circuit 211 may further be configured to output an alarm signal for generating an audible and/or visual indication to an audio/visual output device 288. The alarm signal may indicate one or more of: a partially blocked inlet air duct, a partially blocked exhaust duct, a fouling of a heat exchanger component, a fouling of a combustor component, improper sizing of a duct, or an improper sizing of a duct termination. Alternatively, the alarm signal may be delivered to the combustion controller 12, which may then actuate the audio/visual output device 288. The partial blockage may be significant enough to potentially cause the increased presence of carbon monoxide in the exhaust gases.

FIG. 3 illustrates a graphical example of system pressure operating curves for a typical system.

The system pressures identified in FIG. 3 may be considered typical of a boiler system, such as the boiler system 100 described in the examples of FIGS. 1 and 2. Once a system, such as boiler system 100, is installed, the pressure drop across the system may be a function of various parameters, such as the firing rate, the system configuration and the length, diameter and fittings associated with the inlet and exhaust ducts. FIG. 3 shows the overall boiler system pressure drop and how the differential pressure (i.e. the difference in pressure between the measured inlet (or intake) pressure and the measured exhaust pressure) changes as the duct length increases from the minimum duct length curve 337, a maximum duct length in normal conditions 335, or a maximum duct length with windy conditions shown by curve 333, due to other factors, such as additional back pressure on the boiler system 100.

For example, as long as the pressure differential remains below the heavy solid curve 317, combustion air flow is not adversely effected and combustion remains efficient. When the pressure differential is above curve 317, the combustion efficiency may be reduced resulting in high carbon monoxide emissions. As shown in FIG. 3, even a partial blockage of a boiler duct may adversely affect combustion efficiency and potentially cause the increase in carbon monoxide emissions.

The two different dashed lines 323 and 327 in FIG. 3 below curve 317 illustrate how by having a firing rate dependent pressure interlock, safe operating conditions can be maintained throughout the firing range even for systems with a high turn down ratio. Two possible differential pressure threshold (also referred to as “pressure interlock”) curves are shown: a first differential pressure threshold curve 327 follows the shape of the maximum system pressure, and a second differential pressure threshold curve 323 follows a linear pressure line. Of course, other curve shapes may also be utilized as the differential pressure threshold curve so long as the operating pressure differential remains below curve 317.

Other parameters, such as boiler type, inlet and/or exhaust duct parameters (e.g., length, diameter, fittings or the like), duct termination parameters, fuel type or the like, may be used in the determination of the differential pressure threshold curves.

The comparison of the differential of the measured intakes and exhaust pressures and the pressure differential threshold, or pressure interlock, can be performed, for example, by the digital or analog circuitry of the logic circuit 210/211.

FIG. 4 illustrates an example of how duct blockage effects system performance. The system performance graphic 400 shows a left-hand axis for carbon monoxide in parts per million increasing from the origin upward. The bottom axis represents the percentage duct blockage increasing from zero to one-hundred percent. The right hand axis shows the system pressure differential in inches per water column (labeled as ″ w.c.). For a given firing rate, FIG. 4 illustrates points with respect to pressure differential curve 419, for example, as the inlet or exhaust to the boiler is blocked, the pressure differential, or pressure drop, across the system rises. Eventually at an allowable differential pressure set point, such as point 440, the pressure increase is significant enough to affect the overall combustion air flow and the ability of the combustion control system to maintain the desired air fuel ratio. At point 450, the amount of excess air is reduced leading to incomplete combustion and high carbon monoxide levels. The carbon monoxide values as shown by carbon monoxide curve 414 increase exponentially once this blockage condition is reached. As shown in FIG. 4, even a partial blockage may potentially cause an increase in carbon monoxide emissions.

FIG. 5 illustrates an example of a process flow for detecting an intake or exhaust blockage. In some system examples, there may be redundant pressure sensing elements that are also coupled to the pressure interlock controller. The logic circuit of pressure interlock controller 200/201 may be configured to compare the received values from each of the redundant systems to confirm proper operation of the blockage detection system. The logic circuit of the pressure interlock controller may be further configured to, based on the result of the comparison of the determined pressure differential to a predetermined pressure level differential threshold, identify that a combustion blower of the boiler is operating improperly.

The input signal to the logic circuit from the combustion controller 12 may indicate, for example, the firing rate of the boiler 100 to the pressure interlock controller 19. The input signal to the pressure interlock controller 19 from the exhaust sensing element 18 is representative of the exhaust gas pressure level, and the input signal to the pressure interlock controller 19 from the inlet (or intake) pressure sensing element 17 is representative of the air intake pressure level.

During the execution of the process 500, the logic circuit may be configured, for example, by executing programming code stored in memory, settings in an FPGA or via hardware configuration, to perform some set up to confirm satisfactory operation of the blockage detection system. The operation confirmation process may include steps 510 to 520. During the operation confirmation process, the combustion controller may shut down the combustion process so that no heating is occurring. For example, pressure sensing elements 17 and 18 may provide respective input signals to the logic circuit at 510. An A/D converter (at 515) may convert the analog signals received from the respective pressure sensing elements 17 and 18 into digital signals representative of the pressure signal from the respective pressure sensing element 17 or 18. As part of the system operation confirmation process, the combustion controller may provide a test firing rate, or thermal input, value to the logic circuit. The logic circuit may receive an input from the combustion controller, at 518, to confirm at 520 that the thermal output of the burner is approximately zero. In other words, no heating is occurring and the blower is not outputting any air. In this no-heating and no-blower operational configuration, the inlet air pressure and the exhaust gas pressure is expected to be approximately zero. Based on the inputs from respective pressure sensing element 17 and 18 and the zero firing rate input from the combustion controller, the logic circuit may confirm using a look up table or the like that the differential pressure is approximately zero due to the firing rate (i.e. thermal input) and blower output also being zero. If the differential pressure is determined to be zero, the process 500 proceeds to 525, otherwise, the process 500 proceeds to 555 where a interrupt signal, which indicates a problem with the system, is output and the system is disabled.

When the process 500 proceeds to 525, the logic circuit is configured to receive a test firing rate, or thermal input, signal of one hundred (100) percent, which indicates full burner operation and full blower output. This configuration operates the blower at either a maximum or higher speed that provides increased pressures to confirm operation of the pressure sensors, and also maximum pressure in the air inlet pathway and the exhaust and exhaust variable ducting. The logic circuit receives the inputs from the respective pressure sensing elements 17 and 18, and determines that the differential pressure is within range at the maximum pressures, for example, by using a look up table or the like to confirm operation of the system. If the differential pressure is not within the expected operating range, the process 500 proceeds to 555 where an interrupt signal, which indicates a problem with the boiler system, is output and the boiler system is disabled. This check not only confirms that the pressure sensing elements are working properly but also identifies that the combustion blower is working properly which is a mandated check by most boiler standards. Alternatively, the differential pressure is within the expected operating range, the process 500 proceeds to 530.

In the presence of redundant pressure sensing elements in both the air intake and the exhaust gas outlet, the logic circuit may be configured to compare the differential pressure determined by a first set of pressure sensing elements 17 and 18 to the redundant set of pressure sensing elements 17 and 18. If this comparison is not within tolerances, for example, up to an approximately 10% variation or the like, the process 500 proceeds to 555 where an interrupt signal, which indicates a problem with the system, is output and the system is disabled. Alternatively, if this comparison is within tolerances, the system is operating properly and the system can begin operating to provide heated water, and the process 500 proceeds 525.

A logic circuit may receive a firing rate signal (533) that is variable based on a selected operating range of the boiler system. The logic circuit may also receive (531) additional process parameter signals. For example, the logic circuit additional parameter may be used by the logic circuit to adjust the predetermined pressure level differential threshold at a given firing rate. At 535, the logic circuit may be configured to determine the boiler firing rate based on an input signal from the combustion controller. Based on the determined firing rate (and additional process parameter adjustment signals, if any), the logic circuit may determine a differential pressure threshold that is dependent on the determined firing rate. The differential pressure threshold may be calculated by the logic circuit using a pre-defined curve, such as those shown in FIGS. 3 and/or 4. Alternatively, the logic circuit may access the memory and access a look-up table or the like stored in the memory. The look up table may have predetermined differential pressure threshold settings for each of the variable firing rate inputs from 533 that also account for any process parameter adjustments received at 531. Upon the determination of a differential pressure threshold, the process may proceed to 540. The logic circuit may receive an indication of receive an indication of inlet pressure level from inlet pressure sensing element 17 and receive an exhaust pressure level from pressure sensing element 18.

At 540, the logic circuit may determine a pressure differential between the exhaust pressure level detected by the exhaust pressure sensing element 18 and the inlet pressure level detected by the inlet pressure sensing element 17.

At 550, the logic circuit may compare the determined pressure differential to a predetermined pressure level differential threshold. The logic circuit may determine there is a blockage of an intake or an exhaust of the boiler based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold. For example, the pressure level differential (i.e. an acceptable maximum pressure differential) threshold versus firing rate may be obtained from a pre-defined look-up table or algorithm for the boiler type and size. The logic circuit may use the information in the look-up table and determine there is a blockage. In response to the blockage determination, the logic circuit may output an interrupt signal at 555 that disables the boiler system.

In response to the determination that there is a blockage, the logic circuit may be further configured to output an audible and/or visual indication signal at 555. The output of the audible and/or visual indication signal may cause an audio-visual output device to generate an audio alarm, a visual alarm, or both. The alarm, whether audio or visual, may indicate one or more of: a partially blocked inlet air duct, a partially blocked exhaust duct, a fouling of a heat exchanger component, a fouling of a combustor component, improper sizing of a duct, an improper sizing of a duct termination, or the like.

Alternatively, if the result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold indicates no partial blockage, the process 500 proceeds to 560. At 560, the system is permitted to keep operating. After 560, the process steps 530-550 may repeat to ensure accurate operation of the redundant pressure sensing elements, and that there are no partial blockages.

In the described examples, the differential pressure across (e.g., the differential pressure between an intake duct pressure and an exhaust duct pressure) the boiler system is compared to a predetermined differential pressure threshold, which may also be referred to as a pre-defined, firing rate dependent value. If the differential pressure varies from this pre-defined value, power may be interrupted to the main fuel components thereby preventing the boiler from operating under conditions which may lead to high carbon monoxide in the exhaust gases. The differential pressure may be determined by a single differential pressure sensing transmitter or a combination of transmitters which are used to generate a signal which is proportional to the differential pressure.

Program aspects of the technology discussed above may be thought of as “products” or “articles of manufacture” typically in the form of executable program code and/or associated data (software or firmware) that is carried on or embodied in a type of machine readable medium. “Storage” type media include any or all of the tangible memory of the computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives and the like, which may provide non-transitory storage at any time for the software or firmware programming. All or portions of the programming may at times be communicated through the Internet or various other telecommunication networks. Thus, another type of media that may bear the software/firmware program elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the program code. As used herein, unless restricted to non-transitory, tangible or “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention. 

What is claimed:
 1. A system for detecting blockage of air entering a boiler or exhaust gas exiting the boiler, the system comprising: an exhaust pressure sensing element configured to be coupled to the boiler and to detect an exhaust pressure level of exhaust gas exiting the boiler; an inlet pressure sensing element configured to be coupled to the boiler and to detect an inlet pressure level of air entering the boiler; and a logic circuit coupled to the exhaust pressure sensing element and the inlet pressure sensing element and configured to be coupled to a combustion controller of the boiler, the logic circuit being configured to: determine a firing rate of the boiler based on an input signal received from the combustion controller; determine a pressure differential between the exhaust pressure level detected by the exhaust pressure sensing element and the inlet pressure level detected the inlet pressure sensing element; compare the determined pressure differential to a predetermined pressure level differential threshold, the predetermined pressure level differential threshold being dependent on the firing rate; determine whether a boiler duct is at least partially blocked based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold; and based on a determination that the boiler duct is at least partially blocked, output an interrupt signal; and a relay coupled to the logic circuit, the relay configured to: receive the interrupt signal from the logic circuit, and pupon receipt of the interrupt signal, interrupt power to the combustion controller to shut down a combustion process of the boiler.
 2. The system of claim 1, wherein the logic circuit is further configured to output an alarm signal for generating an audible and/or visual indication indicating one or more of: an at least partially blocked inlet air duct, an at least partially blocked exhaust duct, an at least partial fouling of a heat exchanger component, an at least partial fouling of a combustor component, an improper sizing of a duct, or an improper sizing of a duct termination.
 3. The system of claim 1, wherein the inlet pressure sensing element is coupled to an inlet duct of the boiler.
 4. The system of claim 1, wherein the exhaust pressure sensing element is coupled to an exhaust duct of the boiler.
 5. The system of claim 1, wherein an additional parameter is used to adjust the predetermined pressure level differential threshold at a given firing rate.
 6. The system of claim 1, further comprising: a memory, coupled to the logic circuit, said memory storing the predetermine pressure level differential threshold and program code, wherein the logic circuit is configured to perform functions upon execution of the program code stored in the memory.
 7. A system for detecting blockage of air entering a boiler or exhaust gas exiting the boiler, the system comprising: a differential pressure transmitter configured to: detect a differential pressure across a boiler, and output a pressure differential signal indicating the detected differential pressure across the boiler; a logic circuit coupled to the differential pressure transmitter, the logic circuit being configured to: receive the pressure differential signal from the differential pressure transmitter; compare the pressure differential signal to a predetermined pressure level differential threshold; determine, based upon a result of the comparison of the pressure differential signal to the predetermined pressure level differential threshold, whether there is at least a partial blockage of a duct of the boiler; and in response to a determination of the at least partial blockage of a boiler duct, output a interrupt signal; and a relay coupled to the logic circuit, the relay configured to: in response to receiving the interrupt signal from the logic circuit, halt a combustion process of the boiler.
 8. The system of claim 7, wherein the logic circuit is further configured to: determine a boiler firing rate based on an input signal from a combustion controller, wherein the pressure level differential threshold is dependent on the determined boiler firing rate.
 9. The system of claim 7, wherein the pressure differential signal indicates a negative pressure when an inlet duct is blocked.
 10. The system of claim 7, wherein the pressure differential signal indicates a positive pressure when the exhaust duct is blocked.
 11. The system of claim 7, wherein the comparison between measured system pressure differential and the pre-determined pressure differential is performed via analog circuitry.
 12. The system of claim 7, wherein more than one differential pressure transmitter is utilized as a means to confirm proper operation of the more than one differential pressure transmitters and logic circuit.
 13. The system of claim 7, wherein a second system variable is used to adjust the allowable system pressure drop at a given firing rate.
 14. A method for detecting a blockage in a boiler system, the method comprising steps of: determining, by a logic circuit, a firing rate of the boiler system based on an input signal received from a combustion controller of the boiler system; receiving an indication of exhaust pressure level; receiving an indication of inlet pressure level; determining a pressure differential between the exhaust pressure level and the inlet pressure level; comparing the determined pressure differential to a predetermined pressure level differential threshold, wherein the threshold is dependent on the determined firing rate; determining there is at least a partial blockage of an intake duct or an exhaust duct of the boiler based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold; and in response to the blockage determination, outputting an interrupt signal.
 15. The method of claim 14, further comprising: detecting an exhaust pressure by an exhaust pressure sensing element; outputting the exhaust pressure indication by the exhaust pressure sensing element; detecting an inlet pressure indication by an inlet pressure sensing element; and outputting the inlet pressure indication by the inlet pressure sensing element.
 16. The method of claim 14, further comprising: receiving the exhaust pressure indication via a port coupled to an exhaust outlet tube; and receiving the inlet pressure indication via a port coupled to an inlet tube.
 17. The method of claim 14, further comprising: forwarding the outputted interrupt signal to a relay coupled to the combustion controller.
 18. The method of claim 14, further comprising: determining the predetermined differential pressure threshold by using the determined firing rate and additional parameters, wherein the additional parameters are received from the combustion controller.
 19. The method of claim 14, further comprising: based on the result of the comparison, identifying a combustion blower of the boiler as operating improperly.
 20. A boiler system configured for detecting blockage of air entering the boiler system or exhaust gas exiting the boiler system, the boiler system comprising: a boiler having a combustion controller and a boiler duct; an exhaust pressure sensing element coupled to the boiler and configured to detect an exhaust pressure level of exhaust gas exiting the boiler; an inlet pressure sensing element coupled to the boiler and configured to detect an inlet pressure level of air entering the boiler; and a logic circuit coupled to the exhaust pressure sensing element and the inlet pressure sensing element and the combustion controller, the logic circuit being configured to: determine a firing rate of the boiler based on an input signal from the combustion controller; determine a pressure differential between the exhaust pressure level detected by the exhaust pressure sensing element and the inlet pressure level detected the inlet pressure sensing element; compare the determined pressure differential to a predetermined pressure level differential threshold, the threshold being dependent on the firing rate; determine whether the boiler duct is at least partially blocked based on a result of the comparison of the determined pressure differential to the predetermined pressure level differential threshold; and based on a determination that the boiler duct is at least partially blocked, output an interrupt signal; and a relay coupled to the logic circuit, the relay configured to: receive the interrupt signal from the logic circuit, and in response to receiving the interrupt signal, interrupt power to the combustion controller to shut down the combustion process of the boiler system.
 21. The boiler system of claim 20, wherein the inlet pressure sensing element is coupled to an inlet duct of the boiler.
 22. The boiler system of claim 20, wherein the exhaust pressure sensing element is coupled to an exhaust duct of the boiler.
 23. The boiler system of claim 20, wherein an additional parameter is used to adjust the predetermined pressure level differential threshold at a given firing rate.
 24. The system of claim 20, wherein the determined pressure differential indicates a negative pressure when an inlet duct is blocked.
 25. The system of claim 20, wherein the determined pressure differential indicates a positive pressure when the exhaust duct is blocked.
 26. The boiler system of claim 20, further comprising: a memory, coupled to the logic circuit, said memory storing the predetermine pressure level differential threshold and program code, wherein the logic circuit is configured to perform functions upon execution of the program code stored in the memory.
 27. The boiler system of claim 20, further comprising: the combustion controller, wherein the combustion controller is configured to monitor and control the combustion process of the boiler system. 